Fixes grdp files changes.

md_extensions_strings.grdp was renamed to extensions_strings.grdp
file_manager_strings.grdp was moved to //ui/chromeos - since it's
chromeos specific, don't think we need to bother with it any more.

Chromium changes:

commit 7477b5d6bea903f7ae72d2a2f9483fdfa60a251d
Author: dpapad <dpapad@chromium.org>
Date:   Thu Apr 11 16:35:17 2019 +0000

    Extensions cleanup: Remove "md_" prefix from md_extensions_strings.grdp.

    Bug: 887150

commit 4152f97874932fd5d423ee7d878ba156a40afc88
Author: Luciano Pacheco <lucmult@chromium.org>
Date:   Fri Mar 15 21:34:26 2019 +0000

    Move all Files app translations to //ui/chromeos/

    Follow up from CL: 1476887 where we moved only 1 translation because it
    was after branch freeze.

    This CL moves all Files app translations to //ui/chromeos/ so it can be
    shared with //components/arc and //chromeos/components/drivefs.

build/lib/l10nUtil.js

@@ -38,14 +38,12 @@ const chromiumMediaRouterPartPath = path.resolve(path.join(srcDir, 'chrome', 'ap
 const braveMediaRouterPartPath = path.resolve(path.join(srcDir, 'brave', 'app', 'media_router_strings.grdp'))
 const chromiumSettingsStringsPartPath = path.resolve(path.join(srcDir, 'chrome', 'app', 'settings_strings.grdp'))
 const braveSettingsStringsPartPath = path.resolve(path.join(srcDir, 'brave', 'app', 'settings_strings.grdp'))
-const chromiumMdExtensionsPartPath = path.resolve(path.join(srcDir, 'chrome', 'app', 'md_extensions_strings.grdp'))
-const braveMdExtensionsPartPath = path.resolve(path.join(srcDir, 'brave', 'app', 'md_extensions_strings.grdp'))
+const chromiumExtensionsPartPath = path.resolve(path.join(srcDir, 'chrome', 'app', 'extensions_strings.grdp'))
+const braveExtensionsPartPath = path.resolve(path.join(srcDir, 'brave', 'app', 'extensions_strings.grdp'))
 const chromiumPrintingStringsPartPath = path.resolve(path.join(srcDir, 'chrome', 'app', 'printing_strings.grdp'))
 const bravePrintingStringsPartPath = path.resolve(path.join(srcDir, 'brave', 'app', 'printing_strings.grdp'))
 const chromiumProfileSettingsPartPath = path.resolve(path.join(srcDir, 'chrome', 'app', 'profiles_strings.grdp'))
 const braveProfileSettingsPartPath = path.resolve(path.join(srcDir, 'brave', 'app', 'profiles_strings.grdp'))
-const chromiumFileManagerStringsPartPath = path.resolve(path.join(srcDir, 'chrome', 'app', 'file_manager_strings.grdp'))
-const braveFileManagerStringsPartPath = path.resolve(path.join(srcDir, 'brave', 'app', 'file_manager_strings.grdp'))
 const chromiumVRStringsPartPath = path.resolve(path.join(srcDir, 'chrome', 'app', 'vr_strings.grdp'))
 const braveVRStringsPartPath = path.resolve(path.join(srcDir, 'brave', 'app', 'vr_strings.grdp'))
 const chromiumOnboardingWelcomeStringsPartPath = path.resolve(path.join(srcDir, 'chrome', 'app', 'onboarding_welcome_strings.grdp'))
@@ -76,10 +74,9 @@ const chromiumToAutoGeneratedBraveMapping = {
   [chromiumBookmarksPartPath]: braveBookmarksPartPath,
   [chromiumMediaRouterPartPath]: braveMediaRouterPartPath,
   [chromiumSettingsStringsPartPath]: braveSettingsStringsPartPath,
-  [chromiumMdExtensionsPartPath]: braveMdExtensionsPartPath,
+  [chromiumExtensionsPartPath]: braveExtensionsPartPath,
   [chromiumPrintingStringsPartPath]: bravePrintingStringsPartPath,
   [chromiumProfileSettingsPartPath]: braveProfileSettingsPartPath,
-  [chromiumFileManagerStringsPartPath]: braveFileManagerStringsPartPath,
   [chromiumVRStringsPartPath]: braveVRStringsPartPath,
   [chromiumOnboardingWelcomeStringsPartPath]: braveOnboardingWelcomeStringsPartPath,
   [chromiumAppManagementStringsPartPath]: braveAppManagementStringsPartPath